This invention relates to a method of producing low molecular weight chitin/chitosan and a method of producing an osteoconduction substance and, in particular, to a method of producing low molecular weight chitin/chitosan by irradiation of 60Co γ (cobalt 60 gamma ray) and a method of producing an osteoconduction substance using the low molecular weight chitin/chitosan.
Generally, an osteoconduction substance is used in the field of dental treatment and orthopedics. The osteoconduction substance has a nature of helping or promoting creation of a new bone when it is filled in or around a bone. The osteoconduction substance is excellent in affinity to a tooth and a bone in a human body. The osteoconduction substance has a neutral pH value.
In an existing method of producing an osteoconduction substance, chitin/chitosan is at first dissolved in an acidic aqueous solution to obtain an acidic aqueous solution of chitosan as chitosan sol. The chitosan sol and apatite powder are kneaded together. An acid used in dissolving chitin/chitosan may be acetic acid, lactic acid, malic acid, citric acid, adipic acid, tartaric acid, malonic acid, stearic acid, succinic acid, maleic acid, aspartic acid, and glycin.
The chitosan sol with apatite powder kneaded therein is neutralized by an aqueous solution containing an alkaline compound, such as CaCO3, ZnO, CaO, and CaOH. The chitosan sol after neutralized is solidified in 30 to 60 minutes into the osteoconduction substance having a pH value between 7.0 and 10.0. Thereafter, the osteoconduction substance is dehydrated and stored. The osteoconduction substance after dehydrated is a brittle material.
Prior to use, distilled water or physiological salt solution is absorbed into the osteoconduction substance in order to restore the osteoconduction substance into an elastic body such as rubber.
The osteoconduction substance thus produced is cut into a desired size corresponding to a diseased part of an organism. For example, after operation for periodontitis, the osteoconduction substance is inserted between a jaw bone and a gingiva around a resected site to reconstruct or reproduce the jaw bone.
In the osteoconduction substance containing apatite powder, the apatite powder is neither migrated nor lost. This is because the chitosan sol is transformed into gel so that the apatite powder is appropriately dispersed and fixedly confined in the osteoconduction substance. Before chitin/chitosan is absorbed into an organism, osteoid is effectively grown and substituted for a bone.
However, the existing osteoconduction substance requires a long time to create a new bone.
It is noted here that chitosan has a high molecular weight and is therefore water-insoluble and hardly absorbable into an organism. It is preferable to separate or decompose high molecular weight chitosan into low molecular weight chitosan. This is because chitosan tends to be absorbed by cells as its molecular weight decreases and, as a result, to activate osteoblast cells. For this purpuse, chitosan is subjected to hydrolysis using dense hydrochloric acid. However, this technique requires severe and strict conditions. In addition, it is difficult to control the molecular weight of chitosan.